1. Field of the Invention
The present invention relates to X-rays and, more particularly, is directed towards a method and apparatus for the generation of X-rays.
2. Description of the Prior Art
X-ray tomography for medical diagnostic processes involves the use of a moving source of X-rays for producing either a single cross-sectional density profile of an irradiated subject under diagnosis or a three dimensional density profile from a spatially separated sequence of such cross-sectional profiles. Since it is necessary to irradiate the subject from a large number of different directions in a common cross-sectional plane, the X-ray source encircles or scans the subject for at least one half an orbit and, in many instances, for an entire orbit.
Prior art approaches for moving the X-ray source involve the direct mechnical transport of a standard vacuum X-ray generating tube and its associated high voltage cables. In order to eliminate blurring of the density profile due to subject motion such as respiration and heart beat, it is necessary that the total scan time is made to be substantially less than the time intervals characteristic of such subject motions. Due to the difficulties associated with faster mechanical transport of the X-ray tube, and such associated problems as coiling and uncoiling high voltage cables, attempts at increased scan rates have been met with qualified acceptance. Systems of the type shown in U.S. Pat. No. 3,106,640 for providing a moving source of X-rays by deflecting a rotating beam onto a circular target have been introducted with varying degrees of success.
The need for increased X-rays intensity for maintaining density profile quality has resulted in increased heat production within the X-ray tube. Dissipation of this increase heating, by water cooling for example, becomes impractical with conventional X-ray tubes due to the intended high transport velocity. The use of a rapidly spinning anode, in conjunction with selected beam-on heating time intervals and beam-off cooling time intervals, for heat control and dissipation, which is the present technological state of the art for conventional X-ray tubes, has been met with a limited degree of success.